Labelling machines for automatically performing these operations are well known in the art and their use is widespread in the packaging industry.
In these machines, containers are typically carried by a carrousel along an article path so as to advance towards a labelling station. At the same time, a web of labelling material is fed from a roll-feeding group to a “vacuum drum”, whereby said web is brought into contact with cutting means to be cut into labels of appropriate length. Subsequently, glue is applied on the labels as they are borne by the vacuum drum, e.g. by means of a gluing drum, spray and injector systems or the like. Glued labels are finally transferred from the vacuum drum to the containers.
For proper performance of these operations, accurate handling of the labels is pursued through retention thereof on the surface of the vacuum drum, i.e. by applying vacuum on the labels in a controlled manner. To this purpose, the surface of the vacuum drum comprises a plurality of orifices that can be fluidically connected with a vacuum source.
In particular, this type of labelling process is commonly applied with flexible containers, such as bottles of PET, the use of which is customary in the food and drink industry.
An effort is currently being made, especially in the beverage industry, to lightweight PET containers, with a view to reducing household packaging waste originating, in particular, from the retail sector.
In fact, lightweighting beverage packaging provides a powerful way to minimise waste at source, and to reduce raw material processing and distribution costs. In particular, the energy consumed in the drying of resin and in the melting of PET to make a pre-form and then a bottle is directly related to its weight. Therefore, the potential reduction in energy consumption is proportional to the weight that may avoid being processed.
The weight of PET bottles is determined predominantly by the bottle performance requirements and specification of the neck and base.
In particular, the neck design is influenced by handling requirements, e.g. during filling operations, and by the style of closure used. Different neck finishes have different weights associated with their design features.
The design and weight of the base is mainly related to the requirement to withstand the internal pressure, hence still water bottles can have thinner, and therefore lighter, bases than bottles intended for filling with carbonated beverages.
In general, the mid-section body of a PET bottle has consequently been the obvious focus for manipulation of design for lightweighting, since there are less strict requirements to be accounted for in this respect. In practice, lightweighting has been achieved by pursuing better material distribution during the blow moulding steps, by exploiting novel PET resin compositions and improvements in pre-form heating in blow moulding machines.
However, lightweight PET bottles have a drawback in that they exhibit a peculiar creep behaviour, i.e. they expand quite dramatically with time after filling (especially with carbonated products). Plastics are visco-elastic materials, hence they continue to respond to applied pressures over time, even well after completion of the filling and labelling operations.
Unfortunately, labels, or any other wrapped-type packaging, applied onto the surface of the mid-section body of a lightweight bottle in accordance with the labelling methods known in the art, are highly likely to be severely damaged upon the progressive expansion described above.
The need is therefore felt, in the art, for a method for handling and applying labels to articles travelling along an article path, whereby the drawback described above can be overcome in straightforward and inexpensive fashion.
More particularly, the need is felt for a method for handling and applying labels to articles, whereby lightweight PET bottles can be effectively labelled substantially without the creep-related expansion thereof interfering with the accuracy of application and positioning of the label onto the surface of the mid-section body of the bottles.